Fahrenheit is a temperature scale based on one proposed in 1724 by the Polish-born German physicist Daniel Gabriel Fahrenheit (1686–1736), after whom the scale is named. It uses the degree Fahrenheit (symbol °F) as the unit. There exist several accounts of how he originally defined his scale. The lower defining point, 0 °F, was established as the temperature of a solution of brine made from equal parts of ice and salt. Further limits were established as the melting point of ice (32 °F) and his best estimate of the average human body temperature (96 °F, about 2.5 °F less than modern measurements). The scale is now usually defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, and the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure.
By the end of the 20th century, Fahrenheit was used as the official temperature scale only in the United States (including its unincorporated territories), its freely associated states in the Western Pacific (Palau, the Federated States of Micronesia and the Marshall Islands), the Bahamas, Belize, and the Cayman Islands. All other countries in the world now use the Celsius scale, defined since 1954 by absolute zero being −273.15 °C and the triple point of water being at 0.01 °C
Celsius, also known as centigrade, is a scale and unit of measurement for temperature. As an SI derived unit, it is used by most countries in the world. It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale. The degree Celsius (°C) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature interval, a difference between two temperatures or an uncertainty. Before being renamed to honour Anders Celsius in 1948, the unit was called centigrade, from the Latin centum, which means 100, and gradus, which means steps.
Celsius temperature scale, is based on 0° for the freezing point of water and 100° for the boiling point of water. This scale is widely taught in schools today, by international agreement the unit “degree Celsius” and the Celsius scale are currently defined by two different temperatures: absolute zero, and the triple point of VSMOW (specially purified water).
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